1. Field of the invention
The present invention relates to atomic layer deposition. More particularly, the present invention relates to an apparatus for and process of depositing a thin film on a wafer through atomic layer deposition using remote plasma.
2. Description of the Invention
In general, a semiconductor device is fabricated after conducting a wafer process, an epitaxy process, a thin film deposition process, a diffusion/ion implantation process, a photolithography process, and an etching process. For example, siliceous materials, such as sand, are formed through polycrystalline ingots into monocrystalline wafers which are then subjected to an epitaxy process that involves the deposition of silicon or silicon compounds on the wafer continuing and perfecting the crystal structure of the bare wafer underneath. After the deposition of various thin layers according to their uses, ions are implanted into the wafer and diffused to form devices, followed by dicing the wafer into individual chips. A leadframe is provided to each semiconductor chip which is then sealed with, for example, resin.
At every semiconductor fabrication process are formed various thin films, which are usually classified into four categories: oxides (SiO2) for gate oxides or field oxides; nitrides (Si3N4) for insulation between conductive layers or as masks or element-protecting films upon diffusion/ion implantation; polysilicon films (poly-Si) as gate electrodes instead of metal; and metallic films as electrodes for interconnecting elements to elements or connecting elements to external terminals.
In most cases of forming oxide, nitride and metal thin films, chemical vapor deposition (CVD) is employed. In the semiconductor industry, CVD is useful to form a dense structural part or coating onto a wafer using the decomposition of relatively high vapor pressure gas in a chamber. Gaseous compounds of the materials to be deposited are transported to a substrate surface where a thermal reaction/deposition occurs. Thus far, various CVD methods have been developed as exemplified by atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), plasma enhanced CVD (PECVD), and energy CVD. In any case, the thin film deposited on the substrate should be low in impurities and constant in thickness. Particularly, application of CVD for deposition of metal films results in good step coverage and uniform thickness. In addition, CVD can form metal films on a plurality of wafers. Such a deposition step is very important because it is conducted at almost every semiconductor fabrication step.
Recently, active research has been directed to the application of atomic layer deposition (ALD), a kind of CVD, characterized by the low impurity concentration and constant thickness of the layer deposited, for the fabrication of semiconductor devices.
In conventional ALD, different reactive gases contained in a carrier are alternately fed at predetermined time intervals using a typical bubble method, whereby reaction materials can be transferred to a vacuum chamber where desired metal layers or oxide or nitride films are deposited on wafers. Reactive gases are fed one by one into the vacuum chamber in an alternating manner to form atomic layers on wafers, thereby reducing impurity concentration and controlling the thin film to a desired thickness.
However, such conventional ALD is problematic in that a high temperature is required to heat the reactive material to a suitable temperature or to supply the reactive material with the necessary activation energy and thus, impure thin films are formed to decrease the production yield.
It is therefore an object of the present invention to overcome problems encountered in prior arts and to provide an apparatus for and a process of forming a thin film through atomic layer deposition using remote plasma, which allows the supply of reactive materials (reaction radicals) at such low temperatures as to deposit oxide, nitride and metal thin films almost free of impurities.
In accordance with a first embodiment of the present invention, there is provided an apparatus for depositing a thin film using remote plasma, in which a first reactive gas and a second reactive gas is fed with the aid of a carrier gas into vacuum chamber, comprising: a plurality of transfer pipes for individually transferring the first and the second reactive gas and the carrier gas to the vacuum chamber; an energy supplier, provided inside the transfer pipe for transferring the first and the second reactive gas, for supplying excitation energy to generate excited plasma to ionize the first reactive gas; and a valve controller, established in the transfer pipes, for alternately feeding into the vacuum chamber the second reactive gas and the first reactive gas ionized by the plasma excited in the energy supplier at predetermined time intervals.
In one version of the first embodiment, the energy supplier functions as a plasma generator by generating a high frequency to ionize either the first or the second reactive gas to plasma.
In accordance with a second embodiment of the present invention, there is provided an apparatus for depositing a thin film on a wafer in a vacuum chamber using remote plasma, comprising: a plasma generator for ionizing a first reactive gas to plasma with the excitation energy supplied by a high frequency, said first reactive gas containing N or H; a reactive gas feeder for feeding a second reactive gas; a purge gas feeder for feeding an inert gas; a plurality of valves for feeding the first reactive gas and the second reactive gas in an alternating manner alternately and providing an inert gas between the feeding of the first reactive gas and the second reactive gas, said first reactive gas being ionized by the plasma of the plasma generator; and a valve controller for generating control signals to operate the valves in concert.
In one version of the second embodiment, the first reactive gas is NH3 or H2 and the second reactive gas is provided from a solid source of TaCl5 or a liquid source of TiCl4, Ta(OC2H5)5, SiCl4 or Si2Cl6.
In another version of the second embodiment, the excited, first reactive gas and the unexcited second reactive gas are set to be NH3 and TiCl4, respectively, to form a TiN thin film; NH3 and TaCl5 or Ta(OC2H5)5, respectively, to form a TaN thin film; NH3 and SiCl4 or Si2Cl6, respectively, to form an SiN thin film; and H2 and TaCl5 or Ta(OC2H5)5, respectively, to form a Ta thin film.
In a further version of the second embodiment, the valves comprises: a first feeding valve unit for feeding the unexcited reactive gas to a wafer placed in a vacuum chamber; a second feeding valve unit for feeding to the wafer the gas ionized by the plasma of the plasma generator; and a purge valve unit for feeding a cleaning gas after the operation of the first feeding valve unit and the second feeding valve unit.
Instill a further version of the second embodiment, the excited gas in the plasma generator, the unexcited reactive gas, and the cleaning gas are provided under the control of the valves, and the thin film is deposited by performing a provision cycle consisting of the sequential feeding of the second reactive gas, the cleansing gas, the first reactive gas, and the cleansing gas, once or many times. Herein, the thin film is formed on the wafer to a thickness of ones of Angstrom after one provision cycle and to a desired thickness after one or more provision cycles.
In accordance with a third embodiment of the present invention, there is provided an atomatic layer deposition process using remote plasma, in which a first reactive gas, a second reactive gas, and a carrier gas are fed into a vacuum chamber, comprising the steps of: feeding the first reactive gas, the second reactive gas, and the carrier gas, individually, into the vacuum chamber; ionizing either the first reactive gas or the second reactive gas to plasma; and controlling the flow of gases in such a way that the first reactive gas and the second reactive gas are fed in an alternating manner and the carrier gas is fed between the feeding of the first reactive gas and the second reactive gas.
In accordance with a fourth embodiment of the present invention, there is provided an atomic layer deposition process using remote plasma, comprising the steps of: ionizing a first reactive gas to plasma by use of a high frequency, the first reactive gas containing N or H; preparing an inert gas; preparing an unexcited, second reactive gas; feeding the first reactive gas, the second reactive gas, and the inert gas in such a way that the first reactive gas and the second reactive gas are provided in an alternating manner and the carrier gas is provided between the feeding of the first reactive gas and the second reactive gas, whereby a thin film is formed to a predetermined thickness on a wafer.
In one version of the fourth embodiment, the first reactive gas is NH3 or H2 and the second reactive gas is provided from a solid source of TaCl5 or a liquid source of TiCl4, Ta(OC2H5)5, SiCl4 or Si2Cl6.
In another version of the fourth embodiment, the feeding step is conducted many times.
In a further version of the fourth embodiment, the excited, first reactive gas and the unexcited second reactive gas are set to be NH3 and TiCl4, respectively, to form a TiN thin film; NH3 and TaCl5 or Ta(OC2H5)5, respectively, to form a TaN thin film; NH3 and SiCl4 or Si2Cl6, respectively, to form an SiN thin film; and H2 and TaCl5 or Ta(OC2H5)5, respectively, to form a Ta thin film.